1. Field of the Invention
The present invention relates to an optical communication network apparatus and an optical switching network which are mainly applied to an optical communication field.
2. Description of the Related Art
In order to support a requirement for increasing the capacity of communications, an optical communication network apparatus has recently adopted means for performing wavelength multiplexing to increase the capacity in one optical transmission path. In order to practically use, such a network efficiently has been considered an optical cross-connect system for performing a switching operation on an optical-signal basis at a communication network node to perform drop and insert of an optical signal, which is disclosed by T. Shiragaki et al. in "A Novel Optical Cross-Connect System using Photonic Switch Matrices for Flexible Optical Network Reconfiguration" in Proc. ECOC '93, ThP 5.3, pp.153-156, 1993 (paper 1).
Here, "drop" means that in a network node a signal is output from another communication device of the node concerned, and "insert" means that in a network node a signal from another communication device of the node concerned is convoluted with transmission signal light and then transmitted to another node. In the following description, "pass-through" means that an optical signal transmitted is directly transmitted to another communication device of the node concerned with neither drop nor insert, or transmitted to another node while performing spatially connection switch or vary the wavelength. Further, "wavelength blocking" means that two or more different optical signals are convoluted with each other in the same wavelength in one optical transmission path (optical fiber or the like).
A conventional optical cross-connect node apparatus is disclosed by T. Shiragaki et al. "Optical Cross-connect System using Fixed-Wavelength Converters to Avoid Wavelength Blocking, "First Optoelectronics and Communications Conference (OECC '96) Technical Digest, PD1-5, pp.10-11, 1996) (paper 2), and the construction thereof is shown in FIG. 15.
In the above-described optical cross-connect node apparatus, wavelength multiplexing of m waves is performed on one optical transmission path, and optical transmission paths of n are input/output from another nodes. Therefore, totally m.times.n optical signals are input/output from other nodes. Input terminals 1501 to 150n are connected to front other nodes, and output terminals 1531 to 153n are connected to rear other nodes. Input interfaces 151-1 to 151-m.times.n and output interfaces 152-1 to 152-m.times.n are connected to an electrical digital cross-connect system in the node concerned to receive and transmit signals. Optical signals input from the input terminals 1501 to 150n are subjected to wavelength demultiplexer by wavelength demultiplexer 1541 to 154n and then input to an optical switching network 1599.
The optical signals are switched by the optical switching network 1599 and then input to wavelength converters 1551-1 to 155n-m. The optical signals are subjected to wavelength conversion by the wavelength converters 1551-1 to 155n-m so that no wavelength blocking occurs among the respective output terminals, and then transmitted to the rear other nodes. In order to enable the drop and the insert of all the optical signals in the nodes, the optical switching network 1599 is provided with m.times.n input terminals for the drop and m.times.n output terminals for the insert. Optical signals of m.times.n are input from the rear other nodes and optical signals of m.times.n are input from the input interfaces, so that totally 2m.times.n optical signals are input, and thus 2m.times.n input terminals are provided to the optical switching network 1599. With respect to the output terminals, m.times.n output terminals for transmission to the rear other nodes are provided, and m.times.n output terminals for drop to the node concerned (self node), and thus totally 2m.times.n output terminals are provided to the optical switching network 1599.
In the case of the above-described optical cross-connect node apparatus, the optical signals transmitted can be output to the output terminals which are connected to the output interfaces and the rear other nodes, and the input signals input from the input interfaces can be output to the output terminals. In a network where an optical cross-connect node apparatus is connected to nodes on various routes, it is required that an optical signal coming along any route can be switched to any route and output to any output interface, and an optical signal input from any input interface can be output to any route, and thus such a switching function is needed to the optical switching network work.
However, in order to enable a transmitted optical signal to be output to any output terminal while its wavelength is converted to any wavelength and also to any output interface, and also enable an optical signal input from any input interface to be output to any output terminal while its wavelength is converted to any wavelength, the optical switching network must be provided with non-blocking switching functions of (2m.times.n).times.(2m.times.n). For example, in the case where a matrix switch structure (cross-bar structure) is adopted, a large number of optical switch elements ((2mn).times.(2mn)=4(m.times.n).sup.2 must be provided. Accordingly, an optical communication network apparatus containing an optical switching network thus constructed must be designed in large amount volume and large scale and in high cost.